What does that efficiency metric optimize for? For most americans, switching to public transit means turning their 1-2 hr daily commute into a 3-6 hr. Most americans cannot afford to live in downtowns or near their jobs.
Irrelevant, we don't have those other systems. Invest in them first. Places like NYC have a start, but they don't make good investments in more. Other cities are trying, but have a lot of work to go.
The bigcorp I used to work for provided every employee with a bottomless metro card that could get you a free bus or train ride anywhere in a 20 mile radius. I would guess that maybe 1 in 5 people ever used it. Give someone enough disposable income that they have a choice between a 20 minute ride with their favorite podcast on the stereo vs. a 40 minute ride lurching along with a bunch of strangers and people tend to pick the first one. Our VP, to her credit, did take the bus every day, though.
My point is the ROI of investments in those systems is much higher than trying to improve car infrastructure. And, necessarily, crashes and costs of cars are reduced along the way.
Maybe. If you waste money like NYC does the ROI isn't there. Even if you don't waste money, a small investment won't have enough of a network effect to have a good ROI.